Patent GB-1298061-A (GB)
Title: Improvements relating to target discriminating devices
Inventor: GALE FREDERICK HENRY
IPC: G01J1/42
Filed: 1960-06-09
Abstract: 1298061 Proximity fuses EMI Ltd 1 June 1961 [9 June 1960] 20401/60 Heading F3A [Also in Division H4] A target discriminating device comprises radiation detecting means, means for condensing incident radiation on the detector, and means for providing a predetermined output signal only when the incident radiation affects an area of the detector within prescribed limits of size and within a predetermined time or times. In one arrangement, Fig. 1a, the discrimination is based on the size of the image. The detector is divided into five separate areas, a central area B and four surrounding areas D-G. The output from the central area B may be fed to a fusing circuit through four switches in series, these switches being controlled by the outputs from D-G respectively; thus a fusing signal is produced only if all five areas are energized, and it is assumed that the image of a target P will cover all five areas whilst the image of a spurious source T will cover only the central area. In an alternative arrangement, Fig. 4 (not shown), a detector assembly comprises a lens and three detectors, the two outer detectors performing the function of the areas D-G of Fig. 1a, and a plurality of assemblies are located about the periphery of a missile. In a modification, Fig. 5 (not shown), a single set of three detectors is surrounded by a single optical arrangement which focuses incident radiation from all directions round the axis on to the detectors. The arrangement shown in Fig. 2 comprises a lattice of horizontal and vertical conductors which are connected together at the cross-over points by radiation-sensitive cells. The horizontal conductors are connected to the " two " gates 60 as shown, and the vertical conductors are connected to a counter 59 which applies a voltage pulse to each in sequence. When a pulse is applied to one of the vertical conductors it is applied to all the horizontal conductors, and if any of the cells is energized the pulse is superimposed, on the respective horizontal conductor, on the voltage from the cell. The threshold of gates 60 is adjusted so that a gate will produce an output signal in response to a voltage pulse from the counter when that pulse, as applied to the respective two horizontal conductors, is superimposed on the voltages caused by the simultaneous sensitization of the two cells coupling the vertical conductor and the two horizontal conductors. The output sides of gates 60 are connected through a gate 61 to a storage circuit 62 which has a short rise time and a long decay time and which produces a signal proportional to the sum of the individual pulses received from gate 61 if they follow at the repetition frequency of the counter 59. The amplifier 63 has a threshold such that a signal is produced if the sum output of circuit 62 corresponds to that produced by a predetermined number, e.g. two, of successive pulses from gate 61. In a modified lattice arrangement, Fig. 3 (not shown) each horizontal conductor is connected to a mono-stable device or flip-flop having a time constant greater than the cycle period of the counter. Thus an image on a single radiation-sensitive cell will produce an output on the first scanning cycle but not on the second. The outputs of the mono-stable devices are fed to a frequency discriminator which produces an output if signals recur at the cycle frequency of the counter. This arrangement therefore produces an output signal in response to images which cross the lattice or grow in size at a greater speed than a predetermined minimum.